JN0-363 Service Provider Routing and Switching, Specialist (JNCIS-SP) Questions and Answers

To verify the status of the tunnel from R1, you would issue a ping from the source address that is assigned to R1's end of the tunnel. In the exhibit, we can see that the tunnel interface (gre-0/0/0.0) has the IP address 198.51.100.1 on R1. Therefore, to test the tunnel's status, you should ping the IP address at the other end of the tunnel (which is likely the address on User B's interface or another interface on R2) from R1's tunnel source address.

References:

• Juniper Networks documentation on GRE: GRE Interface Configuration

With Label Distribution Protocol (LDP), a full mesh of label-switched paths (LSPs) is automatically created between all LDP-enabled routers, and these paths are reflected in the inet.3 table. LDP LSPs are set up when LDP is enabled on interfaces connecting routers in an MPLS network.

References:

• Juniper Networks documentation on LDP: Understanding LDP

IS-IS is a link-state routing protocol that uses a Shortest Path First (SPF) algorithm to create a topology map of the network. It floods link-state advertisements (LSAs) to all nodes within the network area to ensure each node has a consistent view of the network topology.

References

• Juniper Networks Technical Documentation on IS-IS
• Understanding IS-IS - Juniper Networks

In BGP (Border Gateway Protocol), the Update message is used to advertise new routes to a peer or to withdraw previously advertised routes. If there's a change in the routing information or if a new route needs to be advertised, BGP uses an Update message. This message is crucial for maintaining the most current and accurate routing information among BGP peers.

The other message types serve different purposes:

Keepalive: This message type is used to maintain the connection between BGP peers and ensure that the link is still active. Keepalive messages are periodically sent between peers when there is no other BGP activity to maintain the session.

Notification: This message is used to indicate errors or other significant events to a BGP peer. If a BGP error condition is detected, a Notification message is sent and the BGP session is typically closed.

Refresh: This is not a standard BGP message type. However, in the context of BGP, Route Refresh is a capability (not a message type) that allows a BGP router to request a full or partial re-advertisement of routes from a peer. This helps in re-synchronizing routing tables without tearing down the BGP session.

The BGP Update message is used to advertise routable destinations and includes route advertisements, route withdrawals, and path attribute modifications. Update messages are used to re-advertise routes that have already been acknowledged.References:

• BGP Operations and Message Types Overview, Juniper Networks Documentation
• BGP Update Message, Juniper Networks Documentation

The adjacency SID in segment routing is advertised by one router to inform another about the label that should be used to forward traffic to it over a particular link. In this scenario, Router B would advertise an adjacency SID to Router A, which would be usedby Router A to forward traffic to Router B. Based on the exhibit, the adjacency SID that Router B advertises to Router A would be 12.

References:

• Juniper Networks documentation on Segment Routing: Segment Routing Overview

In a service provider MPLS network, P routers are interior routers that are used to transit MPLS-labeled packets between edge routers but do not attach or remove MPLS labels themselves. These routers are also referred to as transit routers. They are neither ingress nor egress routers (which are typically labeled as PE routers).

References:

• Juniper Networks documentation on MPLS: MPLS Fundamentals

R2 can not forward IBGP learned routes to another IBGP neighbor correct

R3 will learn about Route X from R2 only. R1 is in a separate AS and Route X is advertised to R2 through eBGP. R2 will then advertise the route to R3 using iBGP. R3 cannot learn routes directly from another AS without having a direct eBGP session with that AS.References:

• BGP Route Propagation and Selection, Juniper Networks Documentation
• Understanding iBGP and eBGP Route Distribution, Juniper Networks Documentation

Theshow bgp neighborcommand in Junos OS provides a detailed description of each BGP session, including session state, options configured, and counters for messages sent and received. This is the command you would use to see a detailed list of all established BGP sessions.

References:

• Juniper Networks documentation on BGP: BGP Commands

Referring to the configuration in the exhibit, R1 is set to export the 3rd_Policy to the neighbor at 192.168.1.5. Since 3rd_Policy permits the 10.200.3.0/24 prefix, only that prefix will be advertised to the neighbor.References:

• BGP Policies, Juniper Networks Documentation
• Policy Framework, Juniper Networks Documentation

only 10.200.3.0/24 will be advertised. The neighbor export overrides anything at the group level and protocol level. Policies aren't additive, you can't apply all three at the same time. What if one of them rejected a prefix while the other accepted the same one? You need one to override the other

The exhibit shows the configuration of a virtual switch calledsw-1with two VLANs defined within it:vlan_1with VLAN ID 1 andvlan_2with VLAN ID 2. To add interfacexe-1/0/5to the virtual switch, the interface must be associated with one of these VLANs. Since the interface is already configured withvlan-id 2, it implies that it is intended to be part ofvlan_2within the virtual switchsw-1. Therefore, the correct answer is to add interfacexe-1/0/5to thevlan_2bridge domain under thesw-1routing instance.

References:

• Juniper documentation on virtual switches: Junos OS Routing Instances Overview

When establishing an EBGP session, it's necessary to specify both the local AS number and the local address that the session will use. The local address is required for establishing the TCP connection for BGP. The local AS must be specified to identify the autonomous system of the router.References:

• Configuring BGP, Juniper TechLibrary
• BGP Peers and BGP Sessions, Juniper TechLibrary

metric—Metric value. Range: 1 through 63, or 1 through 16,777,215 (if you have configured wide metrics) Default: 10 (for all interfaces except lo0), 0 (for the lo0 interface)

static route with a next-hop of next-table pointing to the appropriate routing table which contains more accurate information rib-groups to mirror routing information from one route-table to another. However, in many cases, in order to make this work, interface-routes also need to be mirrored. RIB Group policy can be used to constrain the routing information instance-import and instance-export statements configured within the individual routing-instances to leak routes from one table to another. Again, policy can be used here to constrain the routing information. This method is more straightforward than the rib-group method A final approach is to use physical interfaces or logical-tunnels to stitch routing-instances and use a routing protocol or static routes across this connection between the two routing-instances.

To share routes between two routing instances on a Junos device, you can configure an instance import policy in one or both instances to import routes from the other instance. Alternatively, a RIB (Routing Information Base) group can be used to share routes between instances.References:

• Routing Instances Overview, Juniper Networks Documentation
• RIB Groups Configuration Guide, Juniper Networks Documentation

A Level 1 router can become adjacent with the Level 1 and Level 1-2 (L1/L2) router. A Level 2 router can become adjacent with Level 2 or Level 1-2 (L1/L2) router. There is no adjacency between L1 only and L2 only router. HOWEVER: If two routers are in different areas, they can only form a Level 2 adjacency. As such, two routers in different areas can NOT form a Level 1 adjacency. If you want two routers to form a Level 1 adjacency, they have to be in the same area.

IS-IS (Intermediate System to Intermediate System) operates at two levels: Level 1 and Level 2. Level 1 routers are only aware of their own area's topology, while Level 2 routershave knowledge of the topology across areas. A Level 1 router cannot form an adjacency with a Level 2 router unless the Level 2 router is also operating as a Level 1 router (Level 1-2 router). Level 2 routers can form adjacencies regardless of their area IDs because Level 2 operates at the domain level and is used to interconnect different IS-IS areas.

References

• Juniper Networks Technical Documentation on IS-IS
• IS-IS Levels and Areas Explanation - Juniper Networks

https://www.juniper.net/documentation/us/en/software/junos/high-availability/topics/task/nsr-configuring.html

Nonstop routing (NSR) requires both Graceful Routing Engine Switchover (GRES) and commit synchronization to be configured to maintain routing protocol and forwarding state during a Routing Engine switchover. NSR allows the secondary Routing Engine to take over the control plane without the protocols needing to restart, and GRES ensuresthat the forwarding plane continues operating with the current forwarding table. Commit synchronization ensures that configuration changes are synchronized between the primary and backup Routing Engines.

References:

• Juniper Networks documentation on High Availability: Configuring Nonstop Active Routing

In Ethernet switching, learning and aging are two fundamental concepts for maintaining a dynamic Ethernet switching table (also known as a MAC address table). Learning is the process by which switches listen for frames and learn the MAC addresses by associating them with the incoming port. Aging is the mechanism that ensures the switch updates its table by removing MAC addresses that have not been seen for a certain amount of time (aging time).

References:

• Juniper documentation on Ethernet switching: Understanding Ethernet Switching on Junos OS Devices

The Segment Routing Global Block (SRGB) defines a range of MPLS labels reserved for segment routing. With an SRGB starting label of 10,000 and an index range of 500, the first usable label is indeed 10,001 because label 10,000 is typically reserved and not usedfor forwarding. The last usable label would be 10,499 because the range includes 500 labels starting from 10,001.

References:

• Juniper Networks documentation on Segment Routing: Segment Routing Overview

https://www.catchpoint.com/bgp-monitoring/bgp-attributes

BGP Attribute Categories

There are four categories of BGP attributes:

Well-known mandatory:Recognized by all BGP peers, passed to all peers, and present in all Update messages. Well-known mandatory attributes include:- Next-hop- Origin- AS PATH

Well-known discretionary:Recognized by all routers, passed to all peers, and optionally included in the Update message. Well-known discretionary attributes include:- Local Preference- Atomic Aggregate

Optional transitive:Possibly recognized by BGP routers and passed to BGP peers. Optional transitive attributes are marked as partial when not recognized. Optional transitive attributes include:- Aggregator- Community

Optional non-transitive:Possibly recognized by BGP routers but not passed to peers. Optional non-transitive attributes include:- Multi-exit discriminator (MED)- Originator ID- Cluster-ID

The three well-known mandatory BGP attributes that must be present in every BGP update message are:

• Next Hop: Indicates the next hop IP address to reach the advertising BGP peer.
• Origin: Indicates how the route was originated, whether it was via IGP, EGP, or incomplete.
• AS Path: Lists the autonomous systems that the update has traversed.

References

• Juniper Networks Technical Documentation on BGP Attributes

IPv6 link-local addresses are automatically generated for each interface and have a prefix of fe80::/10. The interface's MAC address is typically used as part of the process to create the Interface Identifier (IID) in the link-local address, following the EUI-64 format.

References

• Juniper Networks Technical Documentation on IPv6
• IPv6 Interface Addresses - Juniper Networks

The IPv6 header includes a new field that is not found in the IPv4 header, called the flow label. The flow label in IPv6 is used to identify packets that require special handling by routers for quality of service (QoS) or other reasons, allowing these packets to be handled efficiently as they move through the network.

References

• Juniper Networks Technical Documentation on IPv6
• IPv6 Header Fields - Juniper Networks

To influence ISP C to prefer the path through R2 for the 172.20.0.0/16 network, R2 should make its path less preferable to ISP B by prepending its AS number multiple times. This makes the path through R2 appear longer and less desirable to ISP C, which would receive these updates from ISP B. AS path length is a well-known attribute in BGP and is used to determine the best path; paths with a longer AS path are considered less preferable.

References:

• Juniper Networks documentation on BGP: BGP Path Selection and Configuration

In IS-IS, Level 1 routes are usually contained within the same area and Level 2 routes are used to interconnect different areas. By default, routes from Level 1 are redistributed into Level 2, and vice versa, to ensure reachability between areas.

References

• Juniper Networks Technical Documentation on IS-IS

By default, IS-IS protocol leaks routing information from a Level 1 area to a Level 2 area. However, to leak routing information from a Level 2 area to a Level 1 area, an export policy must be explicitly configured.